On December 5 & 6 2017, ONERA hosted the first Preliminary Design Review (PDR1) of the project at its Palaiseau site (South Paris, France). This review, which was the 4th Milestone of the project, concludes the 2nd design loop, whose main goal was to refine the design of the system (carrier, launcher and ground segment), with a particular focus on weight reduction and cost-effectiveness. Also, a complete cost study for the whole system was presented for the first time, this task being crucial with regards to the goal of having a competitive and affordable launch system. The results have been presented to European Commission representatives as well as a panel of experts from the space industry and agencies.